Type-III Bifurcation to Chaos in Self-Oscillating States of Squid Giant Axons

This paper describes detailed bifurcation characteristics of firing (time sequence of action potentials) observed in squid giant axons as a function of temperature. The firing is spontaneously induced when the axon is immersed in Ca-reduced ASW (Artificial seawater) without any electrical stimulation. The firing observed above a critical temperature (high-temperature phase firing) is periodic, while the one below the critical temperature (low-temperature) is aperiodic. Our present analysis on the firing shows that aperiodic firing is chaotic, and bifurcation from periodic oscillation to chaos occurs through the type-III intermittency. The type-III bifurcation to chaos should take place through some temperature-dependent properties of the axonal membrane in itself. One of the most probable candidates underlying chaos and bifurcation mechanisms in this experiment could be temperature-dependednt spatial interaction along the longitudinal direction of the squid giant axon.